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View Full Version : What material are boring bars made of?



Elninio
08-22-2010, 03:10 AM
Will it be a bad compromise to make some small boring bars out of cold-rolled round stock (no heat treatment post machining)?

Circlip
08-22-2010, 04:06 AM
Yes it will

mechanicalmagic
08-22-2010, 04:40 AM
Will it be a bad compromise to make some small boring bars out of cold-rolled round stock (no heat treatment post machining)?

Nope, the bending strength of steel in bending makes ~no difference. Use anything you have in the bin. Harden it to your hearts content. Hard IS NOT STIFF.
If you want a bar that is less prone to chatter use Carbide.

Your Old Dog
08-22-2010, 08:25 AM
I have some yard sale special 1" bars. I had no smaller ones so I made them and they work fine with inserts. I thought about using drill rod too if I needed anything too small for the free inserts I have.

BigBoy1
08-22-2010, 08:30 AM
The "Chinese bargain set" of boring bars I got must have been made from plastic, the way the bent and broke! I replace with a USA set and have had no problems.

jep24601
08-22-2010, 10:48 AM
Youngs Modulus of Elasticity for steel is not modified by hardening and remains around 29,000,000 psi.

Plain steel will deflect as much as hardenened steel under load within the elastic region but when it reaches it's yield point it will take a permanent bend. Hardened steel will still spring back to it's original shape when the mild steel has bent.

For a boring bar you want stiffness which comes from mass not hardness. If you were able to bend a mild steel boring bar then it is likely it was deflecting too much anyway and using a hardened steel bar of the same section would likely result in considerable chatter.

radkins
08-22-2010, 11:52 AM
I have also been planing on making a couple of boring bars and the info about hardened or not is something good to know, so what about types of steel such as 4140 or some other alloy?

KiddZimaHater
08-22-2010, 11:55 AM
I used an old, rusty piece of 1018 for an 8 inch boring bar.
It worked like a charm.
.050 depth of cut, 7 inches deep without flinching.

Black_Moons
08-22-2010, 12:19 PM
Yea.. basicly, mild steel might get ruined in a crash/mess up/etc where a hardened steel bar might surive. But.. You should'nt of crashed/messed up in the first place :)

lazlo
08-22-2010, 12:24 PM
Youngs Modulus of Elasticity for steel is not modified by hardening and remains around 29,000,000 psi.

For a boring bar you want stiffness which comes from mass not hardness.

Very well said. To simplify: a mild steel boring bar deflects the same amount as a hardened steel boring bar.

The only advantage of hardening a toolholder is to keep the set screws from biting it.

Al Messer
08-22-2010, 12:30 PM
Will it be a bad compromise to make some small boring bars out of cold-rolled round stock (no heat treatment post machining)?


If the shank is CR and you are using inserts to do the actual cutting, I see no problem, I have made several "bars" out of square 3/8 and 1/2 HR with 1/4 HSS and 1/8 Drill Rod inserts for years with no problems. You have to remember to work the "spring" out with the last few cuts regardless of what material the boring bar setup is made from.

Elninio
08-22-2010, 01:56 PM
Youngs Modulus of Elasticity for steel is not modified by hardening and remains around 29,000,000 psi.

Why is it not modified? I'm not challenging you, just wondering ...

jep24601
08-22-2010, 02:30 PM
Why is it not modified? I'm not challenging you, just wondering ...
Whoah! That's beyond my pay grade. I'm just an engineer - you'll need a metallurgist to answer that question. (Other properties are modified though like ductility and yield strength)

juergenwt
08-22-2010, 02:46 PM
Unless you can find a carbide bar that fits your need your best bet for a long thin boring bar is "Mallory No-chat". This is what professionals use.
Read here:http://www.mallory.com/english/engmats.htm
Or here:www.mallory.com/pdf/DATA%20SHEET%20-%201300.530.pdf

If you are just doing small home type jobs - CRS will do just fine. You just need to take it easy

j king
08-22-2010, 03:02 PM
Here is a bar I made for larger jobs. Got the insert cartridge off ebay. Bought a few so I can change insert style for different opps. These sell cheap on ebay..

http://img.photobucket.com/albums/v24/ikimjing/my%20stuff/carandboringbar013.jpg

http://img.photobucket.com/albums/v24/ikimjing/my%20stuff/carandboringbar017.jpg



Jim

jugs
08-22-2010, 07:38 PM
In a tool room I worked in hundreds of years ago, we used to make chatter free tools from cold roiled mild steel.

The tool was drilled about 7/8 of its length & tapped @ the end, eg: 1" bar drilled 1/2" & tapped 5/8" fine thread, molten lead was poured in leaving 1" of thread, they were left in the canteen freezer over night, a hi-tensile bolt was torqued up cut off flush & welded.

The difference in surface finish between std & the lead damped tools on the same machine was astonishing.

Cheaper than carbide in the bigger sizes.

john
:)

aboard_epsilon
08-22-2010, 07:53 PM
i made some out of mild steel abnout two years ago
here they are ..may give you some idea ...they use chunks of carbide or hss

http://img.photobucket.com/albums/v190/aboard_epsilon/bars.jpg

http://img.photobucket.com/albums/v190/aboard_epsilon/closebar.jpg

all the best.markj

miker
08-22-2010, 09:01 PM
, a hi-tensile bolt was torqued up cut off flush & welded.
john
:)

What is the function of the hi- tensile bolt? Do you braze the cutting tool to it??

Sorry, just can't picture the finished tool:o , but am very interested.

Rgds

j king
08-22-2010, 10:23 PM
Mike . I believe he is saying they tighten the bolt into the end to compress the lead.Puts it in high tension and soaks up vibration with the lead...something like that jim

Elninio
08-23-2010, 12:28 AM
Unless you can find a carbide bar that fits your need your best bet for a long thin boring bar is "Mallory No-chat". This is what professionals use.
Read here:http://www.mallory.com/english/engmats.htm
Or here:www.mallory.com/pdf/DATA%20SHEET%20-%201300.530.pdf

If you are just doing small home type jobs - CRS will do just fine. You just need to take it easy

Very interesting - are 'no-chat' and '1000', identical? They have the same composition, density, and other properties listed in the chart on the first link - but there recommended products are different (one is weight, the other is tool holders).

It must be really expensive though - otherwise entire machines would be made from it?

Elninio
08-23-2010, 12:31 AM
Here is a bar I made for larger jobs. Got the insert cartridge off ebay. Bought a few so I can change insert style for different opps. These sell cheap on ebay..

http://img.photobucket.com/albums/v24/ikimjing/my%20stuff/carandboringbar013.jpg

http://img.photobucket.com/albums/v24/ikimjing/my%20stuff/carandboringbar017.jpg
Jim

Jeez that's <HUGE>. What's your setup, part and machine?

J Tiers
08-23-2010, 12:32 AM
The "Chinese bargain set" of boring bars I got must have been made from plastic, the way the bent and broke! I replace with a USA set and have had no problems.

If those are the "sheep's foot" one-piece type, the chinese (or Indian) parts often have a shank that is a lot smaller than a good USA type. I don't think they control for shank diameter.

The thinner ones will bend if not hard, or break if hard, with considerably less force on them than the thicker ones.

Elninio
08-23-2010, 12:33 AM
In a tool room I worked in hundreds of years ago, we used to make chatter free tools from cold roiled mild steel.

The tool was drilled about 7/8 of its length & tapped @ the end, eg: 1" bar drilled 1/2" & tapped 5/8" fine thread, molten lead was poured in leaving 1" of thread, they were left in the canteen freezer over night, a hi-tensile bolt was torqued up cut off flush & welded.

The difference in surface finish between std & the lead damped tools on the same machine was astonishing.

Cheaper than carbide in the bigger sizes.

john
:)

Would stress relieving the bar after welding weaken it? Why not torque up before the lead solidifies? Wouldn't it be better to cast bismuth instead, since it has a higher modulus of elasticity?

Evan
08-23-2010, 12:53 AM
Why is it not modified? I'm not challenging you, just wondering ...


The hardening produces crystals of iron carbides and/or nitrides. They lie in the interstices of the crystal planes. They make the material harder because the carbides and nitrides are inherently hard materials. When stress is applied they contribute nothing to the strength of the material until the normal elastic limit is reached.

At that point mild steels deform by the sudden slipping of the crystal planes along their boundaries. The stress/strain curve shows a distinct nonlinearity at that point as the material exhibits an increase in strength just before it starts to slip and a decrease after it is slipping.

The addition of the carbides and nitrides ties the crystal planes together so that when the elastic limit is reached the curve goes into the increased strength region and stays there because the planes are not free to slip. It isn't untill the bonds between the iron and the carbides etc are ruptured that deformation takes place.

One note: The stress strain curve for steels is only linear up to the elastic limit. Beyond that point different alloys may have widely different responses to stress. The approximate equality of the response to stress only applies to the linear portion of the stress/strain curve of each alloy.

jugs
08-23-2010, 04:50 AM
Mike . I believe he is saying they tighten the bolt into the end to compress the lead.Puts it in high tension and soaks up vibration with the lead...something like that jim

Correct,
sorry I didn't make that clear :o



Elninio
Would stress relieving the bar after welding weaken it?

Why not torque up before the lead solidifies?

Wouldn't it be better to cast bismuth instead, since it has a higher modulus of elasticity?


The weld was only to cap the stud/bolt to prevent movement.

Lead has twice the expansion/shrinkage rate of steel, hence the freezer, & hi-tensile bolt. As the tool warmed internal pressure on lead would rise.

Lead was easily available (church roof :D ).

john
:)

miker
08-23-2010, 07:56 PM
[QUOTE=aboard_epsilon]i made some out of mild steel abnout two years ago
here they are ..may give you some idea ...they use chunks of carbide or hss

http://img.photobucket.com/albums/v190/aboard_epsilon/bars.jpg

Using the above tools as an example, would they be drilled from the non cutting end then tapped, filled with lead and sealed with high tensile bolt?

jugs
08-23-2010, 08:11 PM
[quote=aboard_epsilon]i made some out of mild steel abnout two years ago
here they are ..may give you some idea ...they use chunks of carbide or hss

http://img.photobucket.com/albums/v190/aboard_epsilon/bars.jpg

Using the above tools as an example, would they be drilled from the non cutting end then tapped, filled with lead and sealed with high tensile bolt?

Yes

john
:)